Recently, with the development of the technology of polycrystalline silicon thin film transistor (TFT), there are more applications of the TFT, and the polycrystalline silicon thin film transistor is considered to be an ideal alternative of an amorphous silicon thin film transistor. In comparison with the amorphous silicon thin film transistor, the polycrystalline silicon thin film transistor has the characteristics of high mobility, high integration, high resolution and so on, thus providing a brighter and finer image.
A thin film transistor known by inventors is usually fabricated by a following method. Referring to FIG. 1, the method comprises: step S1, forming a first passivation layer on a substrate; step S2, depositing an amorphous silicon layer on the first passivation layer, and inducing the amorphous silicon layer so as to form a polycrystalline silicon active layer; step S3, forming a gate insulating layer on the polycrystalline silicon active layer by a patterning process; step S4, forming a gate in a central part above the gate insulating layer; step S5, forming a second passivation layer on the gate insulating layer and the gate; and step S6, forming a source/drain metal layer on the second passivation layer, and forming a source/drain by a patterning process.
The polycrystalline silicon thin film transistors fabricated by above method are formed usually by inducing the amorphous silicon using a crystallization method. In the process of inducing the amorphous silicon to form the polycrystalline silicon, the amorphous silicon crystallizes spontaneously and slowly to form grains along an energy inducing direction. These grains formed in the spontaneous conditions are small in size with random shapes and arrangements, causing low carrier mobility within the polycrystalline silicon.